RFR: 2112: Update JDK to 21 and Gradle to 8.4

Wed Nov 29 23:28:22 UTC 2023

On Wed, 29 Nov 2023 23:18:26 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

> It does appear to work fine however. Our Gradle scripts aren't using Kotlin at all, it's still all Groovy. I would have expected Gradle to protest if it didn't work.

I see others reporting that it's only a problem if you actually use Kotlin in your build scripts here: https://github.com/gradle/gradle/issues/25574

So, I think we are fine with this as long as it works.

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PR Comment: https://git.openjdk.org/skara/pull/1590#issuecomment-1832859238